Communications system capable of communicating encrypted information

ABSTRACT

A communications system for transmitting and receiving information encrypted by a cipher key to and from a remote communication apparatus includes a cipher key storage device for storing a cipher key table in which a plurality of cipher keys and their index numbers are registered and updated. A remote terminal data storage device stores a remote terminal data table including index numbers of the individual cipher keys registered in relation to predefined operation numbers. Input devices are provided for inputting the cipher keys, the index numbers, and the operation numbers. A registration mode setup device is provided for selectively activating a remote terminal data registration mode in which data is registered in the remote terminal data table or a cipher key registration mode in which data is registered in the cipher key table. A registration control device is provided for registering an index number in relation to an operation number in the remote terminal data registration mode and for registering a cipher number in relation to an index number in the cypher key registration mode. Control is provided for automatically switching to plaintext transmission or halting transmission and accepting encryption data when required encryption data is absent.

BACKGROUND OF THE INVENTION

This invention relates to a communications system capable oftransmitting and receiving information in encrypted form to and fromother communications apparatus such as a telephone, radio communicationsequipment or facsimile machine.

In such a communications system, it is desirable to assign a uniquecipher key to each of other communicating user terminals. If, however,the number of user terminals increases, the amount of cipher key databecomes so large that it becomes difficult to manage such data. Oneknown arrangement for facilitating management of cipher key data is toassign a common cipher key to a plurality of other user terminals.

As a known example of communications systems utilizing such anarrangement, one form of facsimile machine is provided with a "cipherkey table" in which a plurality of cipher keys and their index numbersare updatably registered as well as a "user terminal table" in whichindividual users' facsimile numbers, cipher key index numbers, etc. areupdatably registered. With this arrangement, cryptographiccommunications can be automatically performed by using a specifiedcipher key.

In this conventional arrangement, cipher keys are first registered withreference to index numbers in the cipher key table, and then the indexnumbers are registered for individual users in the user terminal table.One problem of this conventional arrangement is its operationalinconvenience in registering data in only one of the two data tables.

Furthermore, if alteration or deletion of data in the cipher key tableand user terminal table is required, an index number in the userterminal table must be altered or deleted at first, and then thecorresponding cipher key in the cipher key table must be altered ordeleted. This is another operability problem of the conventionalarrangement.

It would be possible to reconfigure the above-described conventionalarrangement so that data be separately registered in the cipher keytable and user terminal table. In this modified form of the conventionalarrangement, however, it may happen that although a cipher key indexnumber is registered in the user terminal table, the correspondingcipher key is not registered in the cipher key table. If an instructionis given to perform cryptographic communications in this situation, acommunication error occurs resulting in an inability to communicate.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a communicationssystem which has overcome the aforementioned problems of the prior art.

It is another object of the present invention to provide acommunications system which allows registration, alteration and deletionof data in the cipher key table and user terminal table by simpleoperation, yet enabling communications even when a cipher key is notregistered.

According to the invention, a communications system capable oftransmitting and receiving information encrypted by a cipher key to andfrom other user's communications apparatus comprises cipher key storagemeans for storing a cipher key table in which a plurality of cipher keysand their index numbers are updatably registered; user terminal storagemeans for storing a user terminal table in which index numbers of theindividual cipher keys are updatably registered in relation withpredefined operation numbers; cipher key input means for entering thecipher keys; index number input means for entering the index numbers;operation number input means for entering the operation numbers;registration mode setup means for selectively activating user terminalregistration mode in which data is registered in the user terminal tableor cipher key registration mode in which data is registered in thecipher key table; and registration control means for registering anindex number in relation with an operation number in the user terminaltable when the operation number and index number are entered by theoperation number input means and index number input means, respectively,while user terminal registration mode is selected by the registrationmode setup means, and for registering cipher key in relation with anindex number in the cipher key table when the cipher key and indexnumber are entered by the cipher key input means and index number inputmeans, respectively, while cipher key registration mode is selected bythe registration mode setup means.

In thus constructed communications system, index numbers and cipher keyscan be independently registered in the user terminal table and cipherkey table, respectively, with simple construction. This serves toimprove operating efficiency in registering those data.

The communications system of the invention may be constructed to furthercomprise registration judgment means for judging whether data on theother user or a cipher key corresponding to the other user's indexnumber is registered in the user terminal table or cipher key table; andwarning means for alerting that data on the other user or a cipher keyis not registered when the registration judgment means judges that suchdata or cipher key is not registered.

In this configuration, the warning means produces a warning if it isrequested to communicate when data on the other user or a cipher key isnot registered, prompting an operator of the communications system toregister user data or a cipher key. This would ensure that necessarydata be registered without failure and cryptographic communications beenabled.

The communications system of the invention may be constructed to furthercomprise registration judgment means for judging whether data on theother user is registered in the user terminal table; and communicationsmode setup means for automatically setting the communications system tonormal communications mode when the registration judgment means judgesthat no data on the other user is registered in the user terminal table.

According to this configuration, data is transmitted or received innormal communications mode if execution of a communications task isrequired when no data on the other user is registered in the userterminal table. This would serve to prevent the communications systemfrom becoming unable to communicate.

The communications system of the invention may be constructed to furthercomprise communications mode select means alternatively choosingcryptographic communications mode in which information is transmitted orreceived in ciphertext form or normal communications mode in whichinformation is transmitted or received in plaintext form; registrationjudgment means for judging whether a cipher key for the other user isregistered in the cipher key table in cryptographic communications mode;and communications mode change means for switching the communicationssystem to normal communications mode in accordance with a command fedfrom the communications mode select means when the registration judgmentmeans judges that no cipher key for the other user is registered.

According to this configuration, it is possible to prevent thecommunications system from becoming unable to communicate when no cipherkey for the other user is registered in the cipher key table incryptographic communications mode or the communications system frombeing operated in normal communications mode against an operator'sintention.

The communications system of the invention may be constructed to furthercomprise registration judgment means for judging whether data on theother user or a cipher key corresponding to the other user's indexnumber is registered in the user terminal table or cipher key table; andcommunications mode setup means which temporarily interrupts a currentcommunications process when the registration judgment means judges thatno data or cipher key for the other user is registered, and cancelsinterruption of the communication process when it is verified that userdata or a cipher key has been registered by the registration controlmeans.

According to this configuration, the current communications process istemporarily interrupted if it is requested to communicate when no dataor cipher key for the other user is registered. It is therefore possibleto register the other user's index number or cipher key by using theregistration control means and continue the communications process uponcompleting registration.

In a varied form of the invention, a communications system capable oftransmitting and receiving information encrypted by a cipher key to andfrom other user's communications apparatus comprises cipher key storagemeans for storing a cipher key table in which a plurality of cipher keysand their index numbers are updatably registered; user terminal storagemeans for storing a user terminal table in which index numbers of theindividual cipher keys are updatably registered in relation withpredefined operation numbers; cipher key input means for entering thecipher keys; index number input means for entering the index numbers;operation number input means for entering the operation numbers;alteration request means for requesting alteration of data registered inthe user terminal table or cipher key table; and registered dataalteration means for altering registered index number data if anoperation number and an index number are entered from the operationnumber input means and index number input means, respectively, whenalteration of data registered in the user terminal table is requested bythe alteration request means, and for altering registered cipher keydata if a cipher key and an index number are entered from the cipher keyinput means and index number input means, respectively, when alterationof data registered in the cipher key table is requested by thealteration request means.

In this configuration, it is possible to alter cipher key dataregistered in the cipher key table without altering data registered inthe user terminal table when alteration of data registered in the cipherkey table is requested by the alteration request means. It is alsopossible to alter data registered in the user terminal table withoutaltering data registered in the cipher key table when alteration of dataregistered in the user terminal table is requested by the alterationrequest means.

In a still varied form of the invention, a communications system capableof transmitting and receiving information encrypted by a cipher key toand from other user's communications apparatus comprises cipher keystorage means for storing a cipher key table in which a plurality ofcipher keys and their index numbers are updatably registered; userterminal storage means for storing a user terminal table in which indexnumbers of the individual cipher keys are updatably registered inrelation with predefined operation numbers; deletion request means forrequesting deletion of data registered in the user terminal table orcipher key table; and registered data deletion means for deleting dataregistered in the user terminal table when deletion of such data isrequested by the deletion request means, and for deleting dataregistered in the cipher key table when deletion of such data isrequested by the deletion request means.

In this configuration, it is possible to delete data registered in theuser terminal table without deleting cipher key data registered in thecipher key table when deletion of data registered in the user terminaltable is requested by the deletion request means. It is also possible todelete cipher key data registered in the cipher key table withoutdeleting data registered in the user terminal table when deletion ofcipher key data registered in the cipher key table is requested by thedeletion request means.

These and other objects, features and advantages of the invention willbecome more apparent upon a reading of the following detaileddescription of preferred embodiments, which are illustrated in drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a facsimile machine according to theinvention;

FIG. 2 is a diagram showing a construction of an operating block and adisplay block provided on an operator panel of the facsimile machineaccording to the invention;

FIG. 3 is a circuit diagram of an interface check circuit for verifyinginterface status between the facsimile machine and a personal computer;

FIGS. 4A to 4D are time charts for explaining operation of the interfacecheck circuit;

FIG. 5 is a flowchart showing a routine for checking interconnectionwith the personal computer for any interface errors when the facsimilemachine is switched to personal computer communications (hereinafterreferred to as PC communications) mode;

FIG. 6 is an example of warning message to be displayed in the event ofan interface error;

FIG. 7 is a flowchart showing a routine for checking interconnectionwith the personal computer for any interface errors after the facsimilemachine has been set to PC communications mode;

FIG. 8 is a flowchart showing a routine for periodically checkinginterconnection with the personal computer for any interface errorsafter the facsimile machine has been set to PC communications mode;

FIG. 9 is a flowchart showing operation in user terminal registrationmode;

FIG. 10 is a flowchart showing operation in cipher key registrationmode;

FIGS. 11A and 11B are a first part and a second part of a flowchart,respectively showing data transmission and reception processes infacsimile mode;

FIG. 12 is a flowchart showing how the facsimile machine is switched tofacsimile mode upon completion of printout in PC communications modeaccording to one embodiment of the invention: and

FIG. 13 is a flowchart showing how the facsimile machine is switched tofacsimile mode upon completion of printout in PC communications modeaccording to another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The invention is now described in the following as being embodied in afacsimile machine. It is to be recognized, however, that the facsimilemachine is just an example of communications systems according to theinvention. The invention is applicable to a telephone, radiotransmitter/receiver or any other communications equipment as long as ithas a cipher key table and user terminal table, and index numbers of thecipher key table can be registered as cipher key identification numbersin the user terminal table.

FIG. 1 is a block diagram of a facsimile machine 1 according to theinvention. The facsimile machine 1 is a G3-type facsimile machineconstructed to enable high-speed transmission and reception of encrypteddata.

The facsimile machine 1 has, in addition to the ordinary facsimilefunction, a capability to perform PC communications. For this purpose,the facsimile machine 1 is connected to personal computer 12, whichgives commands necessary for performing PC communications. It is to benoted that the facsimile machine 1 is not necessarily of G3 type, butmay be of G4 or any other type as defined in industry standards.

The facsimile machine 1 comprises a scanner block 2 for reading anoriginal image to be transmitted to other facsimile machine 14, aprinter block 3 for printing image data read by the scanner block 2,image data received from the other facsimile machine 14 or data sentfrom the personal computer 12 on printing paper, a data processing block4 for processing outgoing and incoming image data and PC communicationsdata, a data transfer block 5 for transmitting and receiving data via atelephone line 13, and a control block 6 for controlling the scannerblock 2, printer block 3, data processing block 4 and data transferblock 5.

The control block 6 of the facsimile machine 1 is connected to thepersonal computer 12 via an RS-232C interface 7. Although the presentembodiment employs an interface conforming to the RS-232C standard, thetype of the interface is not limited thereto as long as it allowscommunications between the facsimile machine 1 and personal computer 12.

The control block 6 comprises a data buffer 601 for temporary storage ofPC communications data received from the personal computer 12, aread-only memory (hereinafter referred to as ROM) 602 which stores aprocessing program required for executing facsimile and PCcommunications functions and various kinds of data to be used forcontrolling light source intensity of the scanner block 2 and developingdensity and other operating conditions of the printer block 3 as well asfor presentation of warnings and operating guidance messages, forinstance, and a random access memory (hereinafter referred to as RAM)603 which performs mathematical operations as prescribed in theprocessing program.

The ROM 602 also stores a communications program which enablesinterpretation of AT commands as well as Class 1 and Class 2 commandsestablished and recommended by the Electronic Industries Association(known as EIA) of the United States. The facsimile machine 1 is madecontrollable by AT commands, Class 1 commands or Class 2 commandswhichever entered from the personal computer 12. It is to be noted inthis connection that the choice of commands is not limited to thesethree command systems. Whenever a new command system becomes an industrystandard in future, such a command system may be installed in thefacsimile machine 1 to ensure its general-purpose applicability.

The control block 6 also includes mode reset means which causes thefacsimile machine 1 to be automatically reset from PC communicationsmode to ordinary facsimile mode. The facsimile machine 1 is temporarilyused in a special way (e.g., as a printer) in PC communications mode. Assoon as such a special use of the facsimile machine 1 is finished, themode reset means automatically switches the facsimile machine 1 from PCcommunications mode to facsimile mode to prevent errors in receivingfacsimile messages due to negligence or failure in mode resetting.

The facsimile machine 1 has a command switch 8 for selecting a desiredcommand system. The command switch 8 may be configured with adual-in-line switch (hereinafter referred to as a DIP switch), forexample. As individual "bits" or switch segments of the DIP switch areset to represent a code corresponding to the desired command system, thecode information is read and entered into the control block 6. Thecommand system that controls communications with the personal computer12 is thus selected in accordance with the setting of the command switch8.

The facsimile machine 1 also comprises an operating block 9 includingnumeric keys and one-touch keys, a display block 10 including a liquidcrystal display (hereinafter referred to as LCD) and light-emittingdiodes (hereinafter referred to as LED's), and a speaker 11. Controlsignals for the operating block 9, display block 10 and speaker 11 areinputted to or outputted from the control block 6.

The scanner block 2 contains an automatic document feeder fortransporting a loaded original document, an image pickup unit includinga charge-coupled device (hereinafter referred to as CCD) line imagesensor, and an image processing unit. The image pickup unit scans theoriginal document line by line as it is transported by the automaticdocument feeder. Image data read from the original document is subjectedto image processing including level compensation, gamma correction andanalog-to-digital conversion, and delivered to the data processing block4.

The printer block 3 is built to constitute a laser printer comprising alight projecting unit which emits a laser beam produced by converting amodulating signal derived from pixel data of an image to be printed(hereinafter referred to as print image), a photosensitive unit whichproduces a latent image when subjected to the laser beam emitted by thelight projecting unit, a developing unit which develops the latent imageformed on the photosensitive unit to create a visible print image, animage transfer unit which transfers the visible print image onto paper,and a fixing unit which fixes the transferred print image on the paper.

The data processing block 4 comprises a memory 401 for storing outgoingand incoming data, a compression/expansion circuit 402 for compressingand expanding data, an encryption/decryption circuit 403 for encryptingoutgoing data and for decrypting incoming data, and a data processingcircuit 404 for controlling the memory 401, compression/expansioncircuit 402 and encryption/decryption circuit 403.

The memory 401 is a large-capacity memory device that can store imagesof about 100 pages of A4-size standard documents. This memory enablesreception of a facsimile message while transmitting or receiving anothermessage, reception of a confidential message, as well as scheduledtransmissions. The compression/expansion circuit 402 compresses outgoingdata and expands incoming data according to data compression methods asdefined by Recommendation V.42 bis of the International Telegraph andTelephone Consultative Committee (CCITT).

The encryption/decryption circuit 403 performs data encrypting anddecrypting operations by using predefined cipher keys. The facsimilemachine 1 thus constructed has the capability to encrypt and decryptdata by a substitution cipher method and to transmit and receive suchdata. More specifically, when outgoing data and a cipher key are enteredfrom the data processing circuit 404, the encryption/decryption circuit403 converts the data into ciphertext word by word using the cipher key.Also, the encryption/decryption circuit 403 converts incoming dataencrypted word by word into plaintext.

The RAM 603 of the control block 6 serves as memory means for storing acipher key table, of which example is shown in Table 1. In this example,the cipher key table includes cipher numbers and 10-digit numericalcipher keys. The cipher numbers correspond to the previously mentionedindex numbers of the cipher key table. It would be understood from Table1 that 10 different cipher keys can be registered in this embodiment. Auser of the facsimile machine 1 can register any arbitrary 10-digitnumeral as a cipher key for each cipher number in Table 1. The user canalso alter or delete cipher keys, should the need arise to do so. In theexample of Table 1, no cipher keys are registered yet for cipher Nos. 3and 9.

                  TABLE 1                                                         ______________________________________                                               No.  Cipher Key                                                        ______________________________________                                               1    0 1 2 3 4 5 6 7 8 9                                                      2    1 1 1 2 2 2 3 3 3 4                                                      3                                                                             4    9 8 5 6 1 2 4 3 8 5                                                      .    .                                                                        .    .                                                                        .    .                                                                        9                                                                             10   1 4 6 7 7 6 4 1 3 5                                               ______________________________________                                    

The data processing circuit 404 applies prescribed data processingtreatment to outgoing data, incoming data or PC communications data inaccordance with control signals from the control block 6, and thentransfers the data or print it out on printing paper.

As an example, facsimile transmission of an original document isexecuted in the following manner. As the scanner block 2 scans anoriginal image, the 404 causes the memory 401 to temporarily storeresultant image data. When a transmission start timing signal is enteredfrom the control block 6, the data processing circuit 404 reads theimage data from the memory 401 and sends it to the compression/expansioncircuit 402. Controlled by the data processing circuit 404, thecompression/expansion circuit 402 compresses the image data at aspecified compression ratio and the encryption/decryption circuit 403encrypts the data in accordance with an encryption command from thecontrol block 6. Then, the data processing circuit 404 outputs theencrypted image data to the data transfer block 5.

Facsimile transmission of PC communications data entered from thepersonal computer 12 is executed by the following procedure. The PCcommunications data is first sent to the data processing circuit 404 viathe control block 6. In accordance with an encryption command from thecontrol block 6, the data processing circuit 404 causes theencryption/decryption circuit 403 to encrypt the PC communications dataand then outputs the encrypted data to the data transfer block 5.

In facsimile reception, the data processing circuit 404 delivers imagedata received via the data transfer block 5 to the memory 401 fortemporary storage. When a print start timing signal is entered from thecontrol block 6, the data processing circuit 404 reads the received datafrom the memory 401 and sends it to the compression/expansion circuit402. Controlled by the data processing circuit 404, theencryption/decryption circuit 403 decrypts the data in accordance with adecryption command from the control block 6 and thecompression/expansion circuit 402 expands the image data at a specifiedexpansion ratio. Then, the data processing circuit 404 causes theprinter block 3 to print out the received data.

If it is required to print out PC communications data entered from thepersonal computer 12 on printing paper, the PC communications data issent to the printer block 3 via the control block 6 and data processingcircuit 404.

The data transfer block 5 contains a modulator/demodulator (hereinafterreferred to as modem) 501 for converting data from digital form toanalog form, and vice versa, and a network control unit (hereinafterreferred to as NCU) 502 for addressing other user terminals andestablishing communications line connections.

The operating block 9 is used for entering facsimile numbers of otheruser terminals and facsimile transmission start/stop commands, forregistering, altering and deleting cipher keys, for registeringone-touch keys and simplified facsimile numbers, and for settingconfidential message reception and various other operation modes.

One-touch keys and simplified facsimile numbers are registered for easyand quick transmission of facsimile messages to particular users. Inthis registration process, receiving users' facsimile numbers,accompanied by user names and cipher key numbers, as required, arememorized in a user terminal table preserved in the internal RAM 603 ofthe control block 6. In other words, the RAM 603 serves &S memory meansfor the user terminal table.

Table 2 shows an example of the user terminal table. One-touch keynumbers in Table 2 correspond to the numbers marked on one-touch keys 16of the operating block 9 shown in FIG. 2, or operation numbers used whensending facsimile messages. In this embodiment, up to 10 user terminalscan be registered for the one-touch keys 16. In the example of Table 2,user names, facsimile numbers and cipher key numbers of recipients areregistered for one-touch key Nos. 1, 5, 6 and 9 while nothing isregistered for one-touch key Nos. 2, 4, 7 and 8. In addition, one-touchkey Nos. 3 and 10 have only registered user names and facsimile numbers,but not any cipher key numbers.

The above cipher key numbers correspond to the cipher numbers, or indexnumbers, shown in Table 1. As an example, cipher key No. 1 correspondingto cipher No. 1 of Table 1 is registered for one-touch key No. 1 inTable 2. Therefore, if one-touch key No. 1 is pressed, cipher key"0123456789" assigned to cipher key No. 1 is selected to encryptoutgoing facsimile data or PC communications data prior to datatransmission. Registration of simplified facsimile numbers is done in asimilar manner to that of one-touch key numbers, where the simplifiedfacsimile numbers define necessary keystrokes.

                  TABLE 2                                                         ______________________________________                                        No.     Recipient                                                                              Cipher Key No.  FAX No.                                      ______________________________________                                        1       A B C D  1               06-764-1111                                  3       X X X X                  03-3456-7890                                 4                                                                             5       Δ Δ Δ Δ                                                        3               06-123-4567                                  6       a b c d  7               06-987-6543                                  7                                                                             8                                                                             9       Δ Δ X X                                                                    8               044-123-9876                                 10      W X Y Z                  078-881-1212                                 ______________________________________                                    

The display block 10 includes an alphanumeric readout for indicatingvarious kinds of text information such as recipient's name, facsimilenumber, activation/deactivation status of cryptographic communications,line connection and transmission status in facsimile transmission, entrydata contents in cipher key and user terminal registration, cipher keynon-registration status in encrypted facsimile reception and status ofcommunications with the personal computer 12, as well as indicators fordisplaying communication error status, operation modes, quality ofreceived images, memory-direct reception, maintenance request and so on.

The display block 10 further includes warning means for providing avisual warning in accordance with judgment results of registrationjudgment means provided in the control block 6. More particularly, theregistration judgment means judges during facsimile transmission andreception whether an index number, a corresponding cipher key and otherdata on the other user are registered in the user terminal table orcipher key table. If the registration judgment means judges that no userdata or cipher key is registered, the warning means of the display block10 produces a visual warning indicating that user data or cipher key isnot registered.

The speaker 11 is used to generate an audible warning and to verballycommunicate part of the aforementioned text information. As an example,an audible warning is generated at the end of facsimile transmission orat the start of facsimile reception. If the registration judgment meansjudges that no user data or cipher key is registered in the userterminal table or cipher key table in cryptographic communications,warning means including the speaker 11 generates a verbal warningmessage indicating that user data or cipher key is not registered.

The operating block 9, display block 10 and speaker 11 are provided onan operator panel 15 of the facsimile machine 1. As shown in FIG. 2,there are 10 one-touch keys 16 on the right-hand side of the operatorpanel 15. Numerals marked on the individual one-touch keys 16 representthe operation numbers, or the previously mentioned one-touch keynumbers.

Provided on the upper-left portion of the operator panel 15 are an LCDreadout 18 constituting part of the display block 10 for indicating textinformation, a plurality of LED indicators 17 arranged above and belowthe LCD readout 18 and a speaker grille 19. Below these facilities thereare arranged select keys 20, numeric keys 21, function keys 22,start/stop keys 23 and so on.

The one-touch keys 16 are multi-function keys. They are configured topermit entry of not only one-touch key numbers but also text informationsuch as recipients' names when registering one-touch keys and simplifiedfacsimile numbers. Specifically, the one-touch keys 16 are used forspecifying a predefined operation number, or one-touch key number on onehand. On the other hand, when input mode is switched by operating afunction key 203 of the select keys 20, the one-touch keys 16 are usedfor entering text information.

The LED indicators 17 include a group of LED's for annunciatingcommunication errors, memory-direct reception, confidential messagereception, maintenance request and so on as well as another group ofLED's for providing indications representative of selected functions ofselect keys 201 and 202.

The LCD readout 18 is constructed in such a manner that text informationincluding a few tens of characters can be displayed on two lines. Aplurality of "dots" are arranged in matrix form at each characterposition so that the LCD readout 18 can show any desired characters bylighting appropriate dots.

The select keys 201 and 202 are used for setting printout density andhalftone levels of received images, for selecting operation modes andfor altering input mode of the multi-function keys for instance. As anexample, the select keys 201 and 202 are used to adjust line density orhalftone gradation levels of photographs.

The function key 203 is used for selecting various operation modesincluding cipher key registration mode and user terminal registrationmode. More particularly, the function key 203 serves as registrationmode setup means for selectively activating user terminal registrationmode in which data is registered in the user terminal table or cipherkey registration mode in which data is registered in the cipher keytable. The function key 203 also serves as communications mode selectmeans for alternatively choosing cryptographic communications mode inwhich information is transmitted or received in ciphertext form ornormal communications mode in which information is transmitted orreceived in plaintext form.

Furthermore, the function key 203 serves as cancellation request meansfor requesting deactivation of user terminal registration mode or cipherkey registration mode, alteration request means for requestingalteration of data registered in the user terminal table or cipher keytable, and deletion request means for requesting deletion of dataregistered in the user terminal table or cipher key table.

The numeric keys 21 are used for entering numeric values such asfacsimile numbers, cipher numbers, cipher key number and simplifiedfacsimile numbers. They serve as index number input means for enteringindex numbers, or cipher numbers, in the user terminal table and cipherkey table, cipher key input means for entering cipher key numbers in thecipher key table, and operation number input means for enteringoperation numbers or simplified facsimile numbers.

The control block 6 comprises registration control means. When anoperation number and an index number (or cipher number) are entered bythe operation number input means comprising the one-touch keys 16 and bythe index number input means comprising the numeric keys 21 while userterminal registration mode is selected by the registration mode setupmeans comprising the function key 203, the registration control meansregisters the index number in relation with the operation number in theuser terminal table. Also when a cipher key and an index number (orcipher key number) are entered by the cipher key input means comprisingthe numeric keys 21 and by the index number input means while cipher keyregistration mode is selected by the registration mode setup means, theregistration control means registers the cipher key in relation with theindex number in the cipher key table.

The control block 6 also comprises communications mode setup means whichautomatically switches the facsimile machine 1 to normal communicationsmode if the registration judgment means judges that no data on the otheruser is registered in the user terminal table during facsimiletransmission or reception, as well as communications mode change meanswhich switches the facsimile machine 1 to normal communications mode inaccordance with a command fed from the communications mode select meansincluding the function key 203 if the registration judgment means judgesthat no cipher key for the other user is registered in the cipher keytable during cryptographic communications.

The control block 6 further comprises communications mode control means.When the registration judgment means judges that no data on the otheruser is registered in the user terminal table or no cipher key for theother user's index number is registered in the cipher key table, thecommunications mode control means temporarily interrupts a currentcommunications process. When it is verified that user data or a cipherkey has been registered by the registration control means, thecommunications mode control means cancels interruption of thecommunication process.

Moreover, the control block 6 comprises registered data alterationmeans. If an operation number and an index number are entered by usingthe operation number input means and index number input means,respectively, when alteration of data registered in the user terminaltable is requested by the alteration request means comprising thefunction key 203, the registered data alteration means alters registeredindex number data corresponding to the specified operation number. Alsoif a cipher key and an index number are entered by using the cipher keyinput means and index number input means, respectively, when alterationof data registered in the cipher key table is requested by thealteration request means, the registered data alteration means altersregistered cipher key data corresponding to the specified index number.

The control block 6 further comprises registered data deletion means.When deletion of data registered in the user terminal table has beenrequested by the deletion request means comprising the function key 203,the registered data deletion means deletes registered user terminaldata. Also when deletion of data registered in the cipher key table hasbeen requested by the deletion request means, the registered datadeletion means deletes registered cipher key data.

The function keys 22 are keys for selecting various operations such asmemory-direct reception by using the memory 401, ordinary facsimiletransmission/reception mode (hereinafter referred to as facsimile mode)and pause/redial operations. At the location of the function keys 22,there is provided mode select means including a mode select key 221 forselecting control mode of the facsimile machine 1. If an operator turnson the mode select key 221, the facsimile machine 1 is switched fromfacsimile mode to PC communications mode, and if the operator turns offthe mode select key 221, the facsimile machine 1 is switched from PCcommunications mode to facsimile mode, for example.

The start/stop keys 23 are used to enter transmission start and stopcommands when a facsimile message is transmitted after entering acomplete facsimile number via the numeric keys 21. When a recipient isspecified by using a one-touch key 16 or a simplified facsimile number,the recipient's facsimile number is automatically dialed to establish acommunications line. In this case, a facsimile message is transmittedwith no need for pressing the start key 23.

Referring again to FIG. 1, the RS-232C interface 7 is for connecting thefacsimile machine 1 to the personal computer 12 via an RS-232C cable.There is provided an interface check circuit in the control block 6 forchecking interface status (or whether communication is possible) betweenthe facsimile machine 1 and personal computer 12 when PC communicationsmode is activated and while the facsimile machine 1 is operating in PCcommunications mode. If any interface error is detected, the displayblock 10 and speaker 11 produce audible and visual warnings.

FIG. 3 is a circuit diagram showing an example of the interface checkcircuit. The interface check circuit shown in FIG. 3 is for detectinginterface errors by examining a data terminal ready signal (hereinafterreferred to as DTR signal) inputted from a DTR terminal of an RS-232Cconnector 71 of the RS-232C interface 7.

The DTR terminal of the RS-232C connector 71 is always pulled up to aHigh level by resistor R1. When the personal computer 12 connected tothe RS-232C connector 71 via the RS-232C cable is powered on, the DTRterminal is turned to a Low level. In other words, the DTR signal is setto a Low level when communication with the personal computer 12 isenabled, a High level when communication with the personal computer 12is disabled. Interface status errors can therefore be detected bychecking the level of the DTR signal. Although Low level and High levelDTR signal states represent communication-enabled and -disabledconditions in this embodiment, the interface check circuit may beconstructed to use reversed signal states.

In FIG. 3, an RS receiver 25 converts the level of the DTR signal anddelivers an output signal practically equivalent to the DTR signal. Agate circuit 26 is for feeding the DTR signal outputted from the RSreceiver 25 to a DATA terminal of a central processing unit (hereinafterreferred to as CPU) 28 when PC communications mode is selected. When atiming signal is entered to a gate terminal G, the gate circuit 26outputs the DTR signal fed from its input terminal IN to its outputterminal OUT.

The interface check circuit is constructed in such a manner that a DTRsignal input timing signal is entered from an RD-RS terminal of the CPU28 to the gate terminal G. When PC communications mode is selected bythe mode select key 221, the CPU 28 transmits an input timing signalfrom the RD-RS terminal and receives the DTR signal. Then, the CPU 28judges from the DTR signal level whether interfacing with the personalcomputer 12 is properly established. If interfacing with the personalcomputer 12 is judged abnormal, the CPU 28 causes the display block 10to show a warning message indicating an interface error and the speaker11 to generate an interface error alarm.

FIG. 5 is a flowchart showing a routine for checking interconnectionwith the personal computer 12 for any interface errors when thefacsimile machine 1 is switched to PC communications mode. If it isrequested by the mode select key 221 to switch the facsimile machine 1from facsimile mode to PC communications mode (YES in Step S1), the CPU28 sends an input timing signal to the gate terminal G of the gatecircuit 26 and receives a DTR signal in return (Step S2). Then, statusof interfacing with the personal computer 12 is judged from the level ofthe DTR signal (Step S3). If interface status is satisfactory (YES inStep S3). PC communications mode is activated and the routine isfinished (Step S4). If any interface error is found (NO in Step S3), theLCD readout 18 shows a warning message like the one shown in FIG. 6 andthe speaker 11 generates an audible alarm to warn of an interface errorstatus, and the routine is finished (Step S5). Although this embodimentproduces both audible and visual warnings against interface errors,modification is possible to give audible-only or visual-only warning.

A D-type flip-flop (hereinafter referred to as D-FF) 27 is a circuit forentering level variations in the DTR signal outputted from the RSreceiver 25 into an INT terminal of the CPU 28 in order that the CPU 28can check the status of interfacing between the facsimile machine 1 andpersonal computer 12 in PC communications mode. An output signal of theRS receiver 25 is entered into a CLK terminal of the D-FF 27 and anoutput signal from a Q terminal of the D-FF 27 is entered into the INTterminal of the CPU 28. A D terminal and PR terminal of the D-FF 27 areset to a High level. A RESET signal outputted from a RESET terminal ofthe CPU 28 is inverted and applied to a CLR terminal of the D-FF 27 forresetting the Q terminal output of the D-FF 27.

FIGS. 4A to 4D are time charts for explaining operation of the D-FF 27.First, the CPU 28 transmits a RESET signal to the D-FF 27 (point A inFIGS. 4A to 4D) to reset the Q terminal output of the D-FF 27. Then, aprocess of checking the status of interfacing between the facsimilemachine 1 and personal computer 12 in PC communications mode iscommenced. If the personal computer 12 is powered off or it becomesimpossible to communicate with the personal computer 12 due to abreakage of a communications cable when the facsimile machine 1 in PCcommunications mode, for instance, the DTR signal changes from a Lowlevel to a High level. At the rising edge of the DTR signal (point B inFIGS. 4A to 4D), an inverted signal (Low level) entered from the Dterminal is outputted from the Q terminal of the D-FF 27 to the INTterminal of the CPU 28. Upon detecting an inversion (or a change from aHigh level to a Low level) of the input signal to the INT terminal, theCPU 28 judges that the personal computer 12 has changed from acommunication-enabled state to a communication-disabled state. The CPU28 then causes the display block 10 and speaker 11 to produce warnings.

FIG. 7 is a flowchart showing a routine for checking interconnectionwith the personal computer 12 for any interface errors after thefacsimile machine 1 has been set to PC communications mode. When PCcommunications mode is selected by the mode select key 221 and thefacsimile machine 1 is set to PC communications mode (YES in Step S10),a RESET signal is entered to the D-FF 27. After the Q terminal output ofthe D-FF 27 has been reset, a process of checking the DTR signal outputfrom the Q terminal is commenced (Step S11).

In Step S12, it is judged from variations in the DTR signal levelwhether any error in interfacing with the personal computer 12 hasoccurred. If an interface error is found (YES in Step S12), the LCDreadout 18 shows a warning message and the speaker 11 generates anaudible alarm to warn of an interface error status (Step S13), and theoperation flow proceeds to Step S14. If no interface error is found (NOin Step S12), the operation flow skips Step S13 and proceeds to StepS14.

In Step S14, a judgment is made as to whether it is requested by themode select key 221 to switch the facsimile machine 1 to facsimile mode.If the judgment result is in the affirmative (YES in Step S14),facsimile mode is activated and the routine is finished (Step S15). Ifswitching to facsimile mode is not requested (NO in Step S14), it isfurther judged from variations in the DTR signal level whether theinterface error has been rectified (Step S16). If the interface errorpersists (NO in Step S16), the operation flow returns to Step S13 toreproduce the interface error warnings. If the interface error hasalready been rectified (YES in Step S16), the interface error warningsare stopped (Step S17) and the operation flow returns to Step S10, fromwhere the above-described routine for detecting errors in interfacingwith the personal computer 12 in PC communications mode is re-executed.

Although the facsimile machine 1 of the present embodiment continuouslymonitors the DTR signal to detect errors in interfacing with thepersonal computer 12 in PC communications mode, the facsimile machine 1may be modified to perform periodic checking of the DTR signal fordetecting interface errors. Such a modification is possible byreconfiguring the circuit of FIG. 3. As an example, after PCcommunications mode has been activated, an input timing signal may beentered to the gate terminal G of the gate circuit 26 at specifiedintervals to deliver the DTR signal the DATA terminal of the CPU 28 sothat the CPU 28 can verify the level of the DTR signal. In this modifiedform of embodiment, the D-FF 27 of FIG. 3 is no longer required so thatthe construction of the interface check circuit is simplified.

FIG. 8 is a flowchart showing a routine for periodically checkinginterconnection with the personal computer 12 for any interface errorsafter the facsimile machine 1 has been set to PC communications mode.

The flowchart of FIG. 8 differs from that of FIG. 7 on the followingpoints. Firstly, Step S11 "START DTR SIGNAL CHECK" of FIG. 7 is replacedby Step S11' "DTR SIGNAL CHECK" in FIG. 8. Secondly, new Steps S10-1 toS10-4 are inserted between Steps S10 and S11'.

When PC communications mode is selected by the mode select key 221 andthe facsimile machine 1 is set to PC communications mode (YES in StepS10), an internal timer Tm of the CPU 28 is reset, a time count value Tcis set, and then the timer Tm starts counting (Steps S10-1 to S10-3).

When the timer Tm has counted the set time Tc (YES in Step S10-4), aninput timing signal is sent to the gate terminal G of the gate circuit26 and the DTR signal is entered to the gate circuit 26 (Step S11'). Atthis point, it is judged from the DTR signal level whether any error ininterfacing with the personal computer 12 has occurred (Step S12).

If an interface error is found (YES in Step S12), the facsimile machine1 produces warnings against the interface error until the error isrectified (loop comprising Steps S12 to S16). When the error status iseliminated (YES in Step S16), the interface error warnings are stopped(Step S17) and the operation flow returns to Step S10, from where theabove-described routine for detecting errors in interfacing with thepersonal computer 12 in PC communications mode is re-executed. If it isrequested to switch the facsimile machine 1 to facsimile mode whileinterface error warnings are produced, facsimile mode is activated andthe routine is finished (Step S15).

Referring now to FIG. 9, operation in user terminal registration mode isdescribed in the following.

When user terminal registration mode is selected by the registrationmode setup means comprising the function key 203 (YES in Step S20), thefacsimile machine 1 is set to user terminal registration mode (StepS21). Then, it judged whether a one-touch key number or a simplifiedfacsimile number has been entered by using any one-touch key 16 ornumeric keys 21 which constitute operation number input means (Steps S22and S23). If the judgment result is in the affirmative (YES in Step S22or S23), the registration judgment means verifies the user terminaltable stored in the RAM 603 to check whether there already exists anydata registered for the entered one-touch key number or simplifiedfacsimile number (Step S24).

If no data is registered yet for the entered one-touch key number orsimplified facsimile number (NO in Step S24), the operation flowproceeds to Step S26, where registration of the other communicating userterminal is started by the registration control means. Specifically, anoperator is prompted to sequentially enter the communicating user name,facsimile number, cipher number, confidential message box number, etc.When entry of all these data has been completed (YES in Steps S26 toS29), the display block 10 displays the entered data for verification(Step S30). It is to be noted, however, that the cipher number andconfidential message box number are optional items. If no numbers areentered for these items, it is judged that neither cryptographiccommunications nor confidential message reception will be executed, andthe other items are registered.

The display block 10 displays the entered data contents until aregistration command is given, allowing the operator to alter the data(loop comprising Steps S26 to S31). When the operator gives aregistration command, the entered user name and other associated dataare registered for the specified one-touch key number or simplifiedfacsimile number in the user terminal table (Step S32), and theoperation flow proceeds to Step S36.

On the other hand, if user data is already registered for the enteredone-touch key number or simplified facsimile number (YES in Step S24),the operation flow proceeds to Step S33, where alteration or deletion ofthe previously registered data is made in accordance with instructionsfrom the alteration request means or deletion request means.Specifically, after the display block 10 has presented the previouslyregistered data, the operator is requested to alter or delete theregistered data. If alteration of the registered data is requested bythe alteration request means comprising the function key 203, theoperation flow proceeds to Step S26. Then, following the same procedureas used when registering new data, the previously registered data in theuser terminal table is altered by the registered data alteration means(Steps S26 to S32).

If deletion of the registered data is requested by the deletion requestmeans comprising the function key 203, all the previously registereddata is deleted by the registered data deletion means (Step S35) and theoperation flow proceeds to Step S36.

Next, it is judged whether cancellation of user terminal registrationmode is requested by the cancellation request means comprising thefunction key 203 (Step S36). If cancellation of user terminalregistration mode is requested (YES in Step S36), user terminalregistration mode is canceled (Step S37) and the operation flow returnsto Step S20. If, however, cancellation of user terminal registrationmode is not requested (NO in Step S36), the operation flow returns toStep S22, from where operation for user terminal registration iscontinued.

Referring now to FIG. 10, operation in cipher key registration mode isdescribed in the following.

When cipher key registration mode is selected by the registration modesetup means comprising the function key 203 (YES in Step S40), thefacsimile machine 1 is set to cipher key registration mode (Step S41)and the operator is requested to enter a password. When the operatorenters a correct password (YES in Step S42, NO in Step S43), it becomespossible to register cipher keys. At this point, the operator isrequested to specify a cipher number. When the operator enters an indexnumber corresponding to a cipher number by using the index number inputmeans comprising the numeric keys 21 (YES in Step S44), the registrationjudgment means verifies the cipher key table stored in the RAM 603 tocheck whether a cipher key is already registered for the entered ciphernumber (Step S45).

If no cipher key is registered yet for the entered cipher number (NO inStep S45), the operation flow proceeds to Step S46, where registrationof a new cipher key is performed. First, the operator is prompted toenter a cipher key. When a cipher key is entered by using the cipher keyinput means comprising the numeric keys 21 (YES in Step S46), the cipherkey is registered for the specified cipher number, or index number, inthe cipher key table stored in the RAM 603 (Step S47). Then, theoperation flow proceeds to Steps S51.

On the other hand, if a cipher key is registered for the entered ciphernumber (YES in Step S45), the operation flow proceeds to Step S48, wherealteration or deletion of the previously registered data is made.Specifically, after the display block 10 has presented the previouslyregistered cipher key data (Step S48), the operator is requested toalter or delete the registered data (Steps S49). If alteration of theregistered data is requested by the alteration request means comprisingthe function key 203, the operation flow proceeds to Step S46. Then, anew cipher key is entered by using the cipher key input means comprisingthe numeric keys 21, and the registered data alteration means registersthe new cipher key for the specified cipher number, overwriting anexisting cipher key in the cipher key table stored in the RAM 603 (StepsS46 and S47).

If deletion of the registered data is requested by the deletion requestmeans comprising the function key 203, a previously registered cipherkey is deleted by the registered data deletion means (Step S50) and theoperation flow proceeds to Step S51.

Next, it is judged from an input signal from the cancellation requestmeans comprising the function key 203 whether cancellation of cipher keyregistration mode requested (Step S51). If cancellation of cipher keyregistration mode is requested (YES in Step S51), cipher keyregistration mode is canceled by registration mode cancellation means(Step S52) and the operation flow returns to Step S40. If, however,cancellation of cipher key registration mode is not requested (NO inStep S51), the operation flow returns to Step S44, from where operationfor cipher key registration is continued.

As seen above, the embodiment includes the registration mode setup meansfor selectively activating user terminal registration mode forregistering data in the user terminal table or cipher key registrationmode for registering data in the cipher key table and the registrationcontrol means for controlling data registration processes depending onhow the registration mode setup means is operated. With thisconfiguration, registration, alteration and deletion of communicatingusers in the user terminal table can be made independently ofregistration, alteration and deletion of cipher keys in the cipher keytable. Operations in user terminal registration mode and cipher keyregistration mode are therefore easy and simple.

As an example, even when no cipher key is registered for a particularindex number, or a cipher number, in the cipher key table, it ispossible to register that cipher number in the user terminal table,without registering a cipher key for the cipher number concerned.

Also, cipher key data already registered in the cipher key table may bealtered or deleted even when the corresponding cipher number isregistered in the user terminal table, without altering or deleting thecipher number registered in the user terminal table.

It is now assumed that an operator uses a one-touch key or simplifiedfacsimile number to send a facsimile message. If the cipher numbercorresponding to the one-touch key or simplified facsimile number is notregistered in the user terminal table, or if the cipher keycorresponding to the cipher number is not registered in the cipher keytable although the cipher number is registered in the user terminaltable, a cipher key unregistered warning is produced when the operatorattempts to commence cryptographic communications. In this case, theoperator is requested to register the cipher number or cipher key, aswill be discussed later.

Referring now to FIGS. 11A and 11B, data transmit/receive operations infacsimile mode will be described in the following.

The facsimile machine 1 is initially set to facsimile mode uponpower-on, and PC communications mode is activated by the operator whennecessary. FIGS. 11A and 11B show an operating procedure to be followedby the facsimile machine 1 when it is set to facsimile mode.

When an original document is loaded to the facsimile machine 1 infacsimile mode (YES in Step S60), the operation flow proceeds to StepS62, from where a facsimile transmission process is executed. If ownfacsimile number is called (YES in Step S61), the operation flowproceeds to Step S61, from where a facsimile reception process isexecuted.

In facsimile transmission, the operator is requested to specify arecipient by entering an appropriate number (Step S62). When a numberhas been entered (YES in Step S62), it is judged whether the operatorused a one-touch key 16 or simplified facsimile number (Step S63). Ifthe recipient's facsimile number was entered with the numeric keys 21without using any one-touch key 16 or simplified facsimile number (NO inStep S63), the facsimile machine 1 is set to normal communications mode,in which data is not encrypted (Step S69), and the operation flowproceeds to Step S70.

If the recipient's facsimile number was entered by using a one-touch key16 or simplified facsimile number (YES in Step S63), the user terminaltable stored in the RAM 603 is verified to check whether data on therecipient is already registered (Step S64). If no data on the recipientis registered (NO in Steps S64), the operation flow proceeds to StepS77, where the communications mode control means temporarily interruptsthe current communications process and a process for registering a userterminal is performed.

Specifically, the operator is alerted to a recipient unregistered statusin Step S77. The alerting includes, for example, an audible warninggenerated by the speaker 11 and such a message as "RECIPIENTUNREGISTERED" shown by the display block 10. Subsequently, theregistration judgment means judges whether the operator has chosen toactivate user terminal registration mode by using the registration modesetup means comprising the function key 203 (Step S78). If the judgmentresult is in the negative (NO in Step S78), the operation flow returnsto Step S62. If the judgment result is in the affirmative (YES in StepS78), the registration control means activates user terminalregistration mode (Step S79) and recipient data is registered (StepS80). Then, interruption of the communications process is canceled andthe operation flow proceeds to Step S64.

If data on the recipient is already registered (YES in Steps S64), theregistration judgment means makes a further judgment as to whether aindex number, or a cipher number, is registered for the recipient (StepS65). If the cipher number is not registered (NO in Step S65), theoperation flow proceeds to Step S69, where the communications modechange means automatically switches the facsimile machine to normalcommunications mode. If the cipher number is registered (YES in StepS65), the registration judgment means verifies the cipher key tablestored in the RAM 603 to judge whether a cipher key is registered forthe cipher number concerned (Step S66).

If a cipher key is registered (YES in Step S67), the facsimile machine 1is set to cryptographic communications mode (Step S68), and theoperation flow proceeds to Step S70. If, however, no cipher key isregistered (NO in Step S67), the operation flow proceeds to Step S81,where the communications mode control means temporarily interrupts thecurrent communications process and a process for registering a cipherkey is executed.

Specifically, the operator is alerted to a cipher key unregisteredstatus in Step S81. The alerting includes, for example, an audiblewarning generated by the speaker 11 and such a message as "CIPHER KEYUNREGISTERED" shown by the display block 10. Subsequently, it is judgedwhether normal communications mode has been chosen by operating thecommunications mode change means (Step S82). If the judgment result isin the affirmative (YES in Step S82), the communications mode controlmeans activates normal communications mode (Step S83), and the operationflow proceeds to Step S70 for executing facsimile transmission.

If normal communications mode is not chosen (NO in Step S82), it isfurther judged whether the operator has chosen to activate cipher keyregistration mode by operating the registration mode setup meansincluding the function key 203 (Step S84). If the judgment result is inthe negative (NO in Step S84), the operation flow returns to Step S62.If the judgment result is in the affirmative (YES in Step S84), theregistration control means activates cipher key registration mode (StepS85). After a cipher key has been registered (Step S86), interruption ofthe communications process is canceled. Then, the facsimile machine 1 isset to cryptographic communications mode (Step S87) and the operationflow proceeds to Step S70 for executing facsimile transmission.

In Step S70, the NCU 502 is connected to the recipient's facsimilemachine 14 via the telephone line 13 and facsimile transmission of theoriginal image is started. More particularly, the scanner block 2 scansthe original image (Step S71) and the resultant image data (or outgoingdata) is encoded by the data processing block 4 (Step S72).

Subsequently, it is judged whether the facsimile machine is set tocryptographic communications mode (Step S73). If cryptographiccommunications mode is activated (YES in Step S73), the outgoing data isencrypted by a predefined encryption algorithm by using the cipher keycorresponding to the specified cipher number (Step S74) and transmittedto the recipient's facsimile machine 14 via the data transfer block 5and telephone line 13 (Step S75). If cryptographic communications modeis not activated (NO in Step S73), the outgoing data is transmittedwithout encryption to the recipient's facsimile machine 14 (Step S75).

Next, it is judged whether there is another original document to betransmitted (Step S76). If there is an or signal document (YES in StepS76), the operation flow returns to Step S71, from where theabove-described process of original image scanning and transmission isre-executed. When there is no more original document loaded to thefacsimile machine 1 (NO in Step S76), it is judged that the facsimiletransmission process has been finished and the operation flow returns toStep S60.

In facsimile reception, the NCU 502 is connected to the transmittingfacsimile machine 14 via the telephone line 13 (Step S90) and thefacsimile machine 1 receives data transmitted from the facsimile machine14 (Step S91). The received data is temporarily stored in the memory 401(Step S92).

Then, it is judged whether the received data is encrypted (Step S93). Ifthe data is not encrypted (NO in Step S93), the facsimile machine 1 isset to normal communications mode (Step S97) and the operation flowproceeds to Step S98, from where a process for printing out the receiveddata is executed. If the received data is encrypted (YES in Step S93),the registration judgment means verifies the cipher key table stored inthe RAM 603 to judge whether cipher key is registered for thetransmitting user (Step S94).

If a cipher key is registered (YES in Step S95), the facsimile machine 1is set to cryptographic communications mode (Step S96), and theoperation flow proceeds to Step S98 for printing out the received data.If, however, no cipher key is registered (NO in Step S95), the operationflow proceeds to Step S104, from where a process for registering acipher key is executed.

Specifically, the operator is alerted to a cipher key unregisteredstatus in Step S104. The alerting includes, for example, an audiblewarning generated by the speaker 11 and such a message as "CIPHER KEYUNREGISTERED" shown by the display block 10. Subsequently, it is judgedwhether cipher key registration mode has been chosen by operating theregistration mode cancellation means (Step S105). If the judgment resultis in the negative (NO in Step S105), the operation flow proceeds toStep S60 without printing the received data.

If cipher key registration mode is chosen (YES in Step S105), theregistration control means activates cipher key registration mode (StepS106) and a cipher key is registered (Step S107). Then, it is judgedwhether the operator has entered a command to print the received data byoperating the function key 203 (Step S108). If there is no print command(NO in Step S108), the operation flow returns to Step S62 withoutprinting the received data. If there is a print command (YES in StepS108), the facsimile machine 1 is set to cryptographic communicationsmode (Step S109) and the operation flow proceeds to Step S98, from wherea process for printing out the received data is executed.

In Step S98, the received data is read out from the memory 401. Then, itis judged whether the facsimile machine 1 is set to cryptographiccommunications mode (Step S99). If the judgment result is in theaffirmative (YES in Step S99), the data processing block 4 decrypt thereceived data (Step S100), and the data is decoded (Step S101). If thejudgment result is in the negative (NO in Step S99), the decryptionprocess of Step S100 is skipped and the received data is decoded in StepS101.

The received data is then printed out on paper by the printer block 3(Step S102). When one page of the received data has been printed out, itis judged whether printout of all the received data has been finished(Step S103). If printout of the received data has not been completed (NOin Step S103), the operation flow returns to Step S102 to print the nextpage of the received data. When all pages of the received data have beenprinted out (YES in Step S103), it is judged that the facsimilereception process is finished and the operation flow returns to StepS62.

As seen above, the facsimile machine 1 judges whether an index numberand other data on the other user are registered in the user terminaltable when transmitting or receiving data in facsimile mode. If suchuser data are not registered yet, the audible and visual warning meansof the facsimile machine 1 produce user terminal unregistered warnings,prompting the operator to register data on the other user in the userterminal table before transmitting a facsimile message. According tothis construction, it is possible to transmit or receive the image databy simple operation even when data on the other user is notpre-registered in the user terminal table.

When transmitting or receiving encrypted image data in facsimile mode toor from another user for whom an index number is already registered inthe user terminal table but a corresponding cipher key is not registeredin the cipher key table, the audible and visual warning means of thefacsimile machine 1 produce cipher key unregistered warnings, promptingthe operator to register a cipher key before transmitting or receivingthe image data. With this construction, it is possible to transmit orreceive the encrypted image data even when a cipher key is notpre-registered in the cipher key table.

In one variation of the embodiment, the facsimile machine 1 may be soconstructed that the registration judgment means judges whether data onthe other user is registered in the user terminal table when beginningeryptographic communications, and if it is judged that the index numberis not registered, the communications mode setup means automaticallyswitches the facsimile machine 1 to normal communications mode.According to this construction, it is possible to prevent communicationfailures from occurring due to "user data unregistered" status.

In another variation of the embodiment, the facsimile machine 1 may beso constructed that if the registration judgment means judges that acipher key corresponding to the index number is not registered in thecipher key table when beginning cryptographic communications, thecommunications mode change means switches the facsimile machine 1 tonormal communications mode according to an operator command. With thisconstruction, it is possible to prevent communication failures fromoccurring due to "cipher key unregistered" status and transmit orreceive in normal communications mode.

In still another variation of the embodiment, the facsimile machine 1may be so constructed that if the registration judgment means judgesthat a cipher key corresponding to the index number is not registered inthe cipher key table when beginning cryptographic communications, thecommunications mode setup means automatically switches the facsimilemachine 1 to normal communications mode. With this construction, therearises such inconvenience that the facsimile machine 1 would communicatein normal communications mode against the operator's intention.Accordingly, the facsimile machine 1 should preferably be constructed insuch a manner that it is switched to normal communications mode when theoperator so requires by operating the communications mode change means.

In yet another variation of the embodiment, the facsimile machine 1 maybe so constructed that if the registration judgment means judges thatdata on the other user or a cipher key corresponding to the other user'sindex number is not registered in the user terminal table or cipher keytable when beginning cryptographic communications, the communicationsmode control means temporarily interrupts the current communicationsprocess and interruption of the communications process is canceled whenuser data or cipher key has been registered. According to thisconstruction, it is possible to easily register user data or cipher keyand continue the interrupted communications process after registration.

Referring now to FIGS. 12 and 13, switching between facsimile mode andPC communications mode is described.

FIG. 12 is a flowchart showing how the facsimile machine 1 is switchedto facsimile mode upon completion of printout in PC communications modeaccording to one embodiment of the invention.

The facsimile machine 1 has a print function, in which the facsimilemachine 1 is pre-assigned with a specific facsimile number. Uponreceiving PC communications data addressed to that facsimile number, thefacsimile machine 1 handles the PC communications data in the same wayas image data received in facsimile mode and prints the data on printingpaper. In a modified form of the embodiment, an extended AT commandsystem may be produced so that printout of PC communications data sentto the facsimile machine 1 is controlled by using extended AT commands.

In PC communications mode, the facsimile machine 1 is placed under thecontrol of the personal computer 12. This means that the facsimilemachine 1 performs various jobs in accordance with commands entered fromthe personal computer 12. Although the facsimile machine 1 worksindependent of the personal computer 12 in facsimile mode, it becomes aperipheral device of the personal computer 12 in PC communications mode.

The facsimile machine 1 works in different ways depending on whichoperation mode is selected. PC communications mode provides asupplementary function to the facsimile machine 1 for supportingcommunications with the personal computer 12 and facsimile mode shouldbe considered as main mode of the facsimile machine 1. It is expectedthat the print function for printing out PC communications data wouldnormally be used just temporarily upon switching the facsimile machine 1from facsimile mode to PC communications mode. Therefore, the presentembodiment is constructed in such a manner that the facsimile machine 1is automatically reset to its main mode (or facsimile mode) when aprinting job in PC communications mode has been completed. Thisconstruction would serve to improve operating efficiency in facsimilemode.

When PC communications mode is selected by the mode select key 221 (YESin Step S110), the facsimile machine 1 is set to PC communications mode(Step S111) and becomes ready to perform PC communications.

When an AT command i s received from the personal computer 12 (YES inStep S112), it is judged whether a printing job is requested by thereceived AT command (Step S113). If a printing job is requested (YES inStep S113), a set of AT commands for execution of the printing job andPC communications data are received (Step S114). Then, the printer block3 sequentially prints out the incoming data on printing paper (loopcomprising Steps S115 and S116). When the printing job is completed (YESin Step S116), the facsimile machine 1 is automatically switched from PCcommunications mode to facsimile mode (Step S117) and the operation flowreturns to Step S110.

If a printing job is not requested in Step S113, a set of AT commandsand PC communications data are received (Step S118) and a specifiedcommunications process is carried out in accordance with the received ATcommands (Step S119). Next, it is judged whether facsimile mode isselected by the mode select key 221 in Step S120. If facsimile mode isselected (YES in Step S120), the operation flow proceeds to Step S117,where the facsimile machine 1 is set to facsimile mode (Step S117) andthe operation flow returns to Step S110. If facsimile mode is notselected (NO in Step S120), the facsimile machine 1 remains in PCcommunications mode and the operation flow returns to Step S112, wherethe facsimile machine 1 waits for a next command.

As seen above, the facsimile machine 1 is so constructed that a printingjob is executed in accordance with AT commands sent from the personalcomputer 12 only when the facsimile machine 1 is switched from ordinaryfacsimile mode to PC communications mode by the mode select meanscomprising the mode select key 221 and the facsimile machine 1 isswitched to facsimile mode immediately after confirming that theprinting job has been completed. With this arrangement, the facsimilemachine 1 is automatically switched from PC communications mode tofacsimile mode after executing PC communications, and there is no needto operate the mode select key 221 of the facsimile machine 1 which isplaced apart from the communications system including the personalcomputer 12. This would serve to allow efficient use of the facsimilemachine 1.

Unlike a conventional facsimile machine which remains in PCcommunications mode unless a mode select switch is operated, thefacsimile machine 1 is automatically reset to facsimile mode uponcompleting a printing job in PC communications mode so that it canreceive image data transmitted from the other facsimile machine 14without failure.

According to the above-described embodiment, the facsimile machine 1 isunconditionally switched back to facsimile mode upon completion of theprinting job. The embodiment may be modified to include mode resettinginhibit means which inhibits automatic switching from PC communicationsmode to facsimile mode until a mode resetting command signal isoutputted from the personal computer 12, as shown in FIG. 13. Moreparticularly, the flowchart of FIG. 13 contains an additional Step(S116-1) for judging whether the personal computer 12 has outputted amode resetting command signal including an extended AT command afterStep S116 shown in the flowchart of FIG. 12.

The aforementioned extended AT command is a user-defined command addedto the standard AT command system. The extended AT command used in StepS116-1 is a command for switching the facsimile machine 1 from PCcommunications mode to facsimile mode upon completion of a printing job.This extended AT command is added to the end of a set of AT commands forexecution of the printing job and sent to the facsimile machine 1.

In FIG. 13, the facsimile machine 1 is set to PC communications mode andreceives a set of AT commands concerning the printing job and data inSteps S110 to S114. Upon completion of printout of the received data(Steps S115 and S116), it is judged whether the extended AT command AT8requesting automatic mode switching has been received (Step S116-1). Ifautomatic mode switching of the facsimile machine 1 is requested (YES inStep S116-1), the facsimile machine 1 is set to facsimile mode (StepS117) and the operation flow returns to Step S110. If, however,automatic mode switching of the facsimile machine 1 is not requested (NOin Step S116-1), the facsimile machine 1 remains in PC communicationsmode and the operation flow returns to Step S112, where the facsimilemachine 1 waits for a next command.

Although the embodiments of FIGS. 12 and 13 employ the AT commandsystem, it is possible to handle the communications process by the useof other suitable command systems.

As seen above, the facsimile machine 1 is constructed to inhibit itsswitching from PC communications mode to facsimile mode until a moderesetting command signal is outputted from the personal computer 12.According to this construction, it is possible to effectively preventdeterioration of operating efficiency due to frequent switching from PCcommunications mode to facsimile mode that will otherwise occur uponcompletion of printout even when the operator intends to stay in PCcommunications mode.

In an alternative form of the invention, the function keys 22 mayinclude a command key that will constitute command means for choosingwhether to perform automatic resetting of the facsimile machine 1 fromPC communications mode to facsimile mode so that automatic moderesetting is made only when it is requested by operating the commandmeans, and otherwise inhibited by the mode resetting inhibit means. Withthis alternative construction, the flowchart of FIG. 13 should bemodified so that a judgment is made in Step S116-1 to check whetherautomatic mode resetting is requested by the command means.

According to the embodiment described above, the facsimile machine 1 isprovided with interface check means comprising the interface checkcircuit for verifying interface status between the facsimile machine 1and personal computer and when an interface error is found, the warningmeans comprising the display block 10 and speaker 11 produce audible andvisual warnings. With this arrangement, it is possible to take anappropriate remedial action immediately when an interface error occursin PC communications mode. This serves to reduce time periods duringwhich the facsimile machine 1 does not actually function in PCcommunications mode and enable efficient use of the facsimile machine 1.

Furthermore, the above embodiment is so constructed that the interfacecheck means checks for interface errors after confirming that theoperator has operated the mode select means comprising the mode selectkey 221 for switching the facsimile machine 1 from facsimile mode to PCcommunications mode. With this arrangement, it is possible for theinterface check means to check interface status at an optimum point oftime when it has become certain that the facsimile machine 1 is going tobe used as a peripheral device of the personal computer 12.

In the embodiment shown in FIG. 8, the interface check meansperiodically checks for interface errors after the operator has operatedthe mode select means comprising the mode select key 221 for switchingthe facsimile machine 1 from facsimile mode to PC communications mode.This arrangement is advantageous in that the interface check means canbe simplified in its construction compared to an arrangement in whichthe interface check means continuously checks for interface errors.

What is claimed is:
 1. A communication system for transmitting andreceiving information encrypted by a cipher key to and from a remoteterminal, said communication system comprising:cipher key storage meansfor storing and updating a cipher key table having a plurality of cipherkeys and index numbers corresponding thereto; remote terminal datastorage means for storing and updating a remote terminal table havingremote terminal data including index numbers, corresponding to thecipher keys, registered in relation to predefined operation numberscorresponding to respective remote terminals; cipher key input means forentering the cipher keys; index number input means for entering theindex numbers; operation number input means for entering the operationnumbers; registration mode setup means for selectively activating aremote terminal registration mode in which said remote terminal data isregistered in the remote terminal table or a cipher key registrationmode in which data is registered in the cipher key table: andregistration control means for registering an index number incorrespondence with an operation number in the remote terminal tablewhere the operation number and the index number are entered by saidoperation number input means and said index number input means,respectively, while said remote terminal registration mode is selectedby said registration mode setup means, and for registering a cipher keyin correspondence with an index number in the cipher key table where thecipher key and the index number are entered by said cipher key inputmeans and said index number input means, respectively, while said cipherkey registration mode is selected by said registration mode setup means.2. A communication system according to claim 1, furthercomprising:registration verification means for determining whetherremote terminal data or a cipher key corresponding to an index number isregistered in the remote terminal table or said cipher key table; andwarning means, responsive to said registration verification means, forindicating that remote terminal data or a cipher key is not registered.3. A communication system according to claim 1, furthercomprising:registration verification means for determining whetherremote terminal data corresponding to a specified remote terminal isregistered in the remote terminal table; and communications mode setupmeans for automatically setting said communications system to a normalcommunications mode when said registration verification means determinesthat said remote terminal data corresponding to said specified remoteterminal is not registered in the remote terminal table.
 4. Acommunication system according to claim 1, furthercomprising:communications mode selection means for alternativelychoosing a cryptographic communications mode in which information istransmitted or received in ciphertext form or a normal communicationsmode in which information is transmitted or received in plaintext form;registration verification means for determining whether a cipher key fora selected one of said remote terminals is registered in the cipher keytable when said communication system is in said cryptographiccommunications mode; and communications mode change means for switchingsaid communications system to said normal communications mode inaccordance with a command from said communications mode select meanswhen said registration verification means judges that no cipher key forsaid selected one of said remote terminals is registered.
 5. Acommunication system according to claim 1, furthercomprising:registration verification means for determining whetherremote terminal data or a cipher key corresponding to an index numberfor a selected one of said remote terminals is registered in the userterminal table or the cipher key table; and communications mode setupmeans, responsive to said registration judgment means for temporarilyinterrupting a current communications process when said registrationverification means determines that no remote terminal data or cipher keyfor said selected one of said remote terminals is registered, and forcancelling interruption of the current communication process when saidregistration verification means determines that remote terminal data ora cipher key is registered by said registration control means.
 6. Acommunication system for transmitting and receiving informationencrypted by a cipher key to and from a remote terminal, saidcommunications system comprising:cipher key storage means for storingand updating a cipher key table having a plurality of cipher keys andindex numbers corresponding thereto; remote terminal data storage meansfor storing and updating a remote terminal table having said indexnumbers corresponding to the individual cipher keys storable in relationto predefined operation numbers; cipher key input means for entering thecipher keys; index number means for entering the index numbers;operation number input means for entering the operation numbers;alteration request means for requesting alteration of data in the remoteterminal table or the cipher key table; and data alteration means foraltering registered index number data when an operation number and anindex number are entered from said operation number input means and saidindex number input means, respectively, when alteration of data in theremote terminal table is requested by said alteration request means, andfor altering cipher key data if a cipher key and an index number areentered from said cipher key input means and said index number inputmeans, respectively, when alteration of data in the cipher key table isrequested by said alteration request means.
 7. A communication systemfor transmitting and receiving information, encrypted by a cipher key,to and from a remote terminal, said communication systemcomprising:cipher key storage means for storing and updating a cipherkey table having a plurality of cipher keys and index numberscorresponding thereto; remote terminal data storage means for storingand updating a remote terminal data table having index numberscorresponding to the individual cipher keys storable in relation topredefined operation numbers; deletion request means for requestingdeletion of data registered in the remote terminal data table or thecipher key table; and registered data deletion means for deleting dataregistered in the remote terminal data table when deletion of such datais requested by said deletion request means, and for deleting dataregistered in the cipher key table when deletion of such data isrequested by said deletion request means.